The invention relates to a method that is intended for regenerating a compressed air supply device of a commercial vehicle (also known as a utility vehicle) and that supplies a first compressed air circuit with compressed air. The compressed air from the first compressed air circuit is used to regenerate the compressed air supply device. In addition, the present invention relates to a method for regenerating a compressed air supply device of a commercial vehicle, the compressed air supply device being configured so as to supply a first compressed air circuit and a second compressed air circuit. In addition, the present invention relates to an electronic control unit that is intended for a compressed air device of a commercial vehicle and that is configured so as to control one of the methods according to the invention, as well as to a compressed air supply device with such an electronic control unit.
Compressed air supply devices fulfill important tasks in commercial vehicles, for example, in trucks and tractors. There is typically a compressor that draws in the ambient air. However, such ambient air usually contains a relatively high amount of moisture and other deleterious constituents that should not be fed to the compressed air consumers. In order to prevent especially too moist air from being fed to the air consumers, the compressed air supply devices typically have a filter unit with an air dryer for dehumidifying the intake air. The air flows through the air dryer, which is generally provided with an air dryer cartridge that removes the moisture from the air flowing through the air dryer cartridge. Other deleterious constituents can also be filtered out of the air in the filter unit. Then the dried and filtered air is fed to the compressed air consumers, such as the service brake system, a parking brake with spring energy accumulators, an air suspension of the vehicle or compressed air consumers of a trailer.
The more air that is conveyed through the air dryer, the more moisture collects in the air dryer or, more particularly, the air dryer cartridge. However, the air dryer's holding capacity for moisture is limited and eventually reaches a saturation level.
When the saturated moisture level of an air dryer or, more particularly, of an air dryer cartridge has been reached, the air dryer cartridge cannot hold any more moisture, so that the air that continues to flow through the air dryer cartridge is fed in an undried state into the compressed air consumer circuits, a state that can have a negative impact on the functionality of the compressed air consumer systems.
Therefore, compressed air supply devices are regenerated. During a regenerating process the compressed air flow is reversed in the air dryer, for example, by discharging the compressed air from the supply tank of one of the compressed air circuits of the commercial vehicle through the air dryer into the atmosphere. As the air flows through the air dryer into the regenerating device, the air flowing through removes the moisture and any other foreign particles from the filter and the air dryer. Hence, such a regenerating process consumes compressed air and, therefore, results in a drop in pressure in the compressed air reservoir, from which the regenerating compressed air comes.
However, when the air dryer reaches its saturation level, the air that flows through the air dryer for the purpose of supplying the compressed air consumers is not further dehumidified, that is, moist air will be conveyed to the compressed air consumers. If during a regenerating process this moist air is conveyed through the air dryer into the regenerating device, the result is only limited regeneration, because the air dryer cartridge cannot efficiently dry the moist regenerating air. Hence, an air dryer that has reached its saturated moisture level can no longer fulfill not only its task of dehumidifying the supply air, but it can also dry or rather regenerate the supply air only with difficulty and very slowly.
In modern commercial vehicles the compressed air reservoir of the various compressed air consumer circuits is often filled before driving off. In this case the conventional practice is to regenerate once the compressed air supply device, when the service brake system of a commercial vehicle is raised to maximum pressure. In so doing, the compressed air from the service brake system is used that is thereafter raised to the maximum pressure again. The maximum filling pressure of a service brake system of a commercial vehicle is typically 12.5 bar. The regeneration process is usually carried out until there is a predetermined pressure loss in the service brake system, so that the pressure in this system is decreased, for example, to 11 or 10 bar.
However, it can happen in commercial vehicles with a very high compressed air consumption that despite the conventional regeneration processes the air dryer reaches a very high moisture level or even a saturated moisture level. For example, commercial vehicles that have a container lifting device, but travel only short distances, such as vehicles for transporting containers at harbor facilities, use pneumatic lifting systems with up to 15 bar. Owing to the frequent lifting and lowering operations, such vehicles have such a high requirement of compressed air flow through the air dryer that a conventional air dryer cartridge quickly reaches the saturation level.
One way of preventing the air dryer in commercial vehicles with a high compressed air consumption from rapidly reaching a saturation level consists of increasing the dehumidifying capacity of the air dryer cartridge. This increase can be achieved, in particular, by increasing the dimensions of the air dryer cartridge. However, the development of larger air dryer cartridges is expensive, because as the size of the throughflow areas for the air stream increases, the forces exerted on the elements of the air dryer cartridge become significantly larger. In addition, the time required for a larger air dryer cartridge for drying increases if it were to be wetted up to the saturation level.
Therefore, there is a need for an improved method and for an improved compressed air supply device that together circumvent the problem of the air dryer reaching a moisture level that is too high and, in particular, of the air dryer reaching a saturated moisture level.
According to this specification, the first compressed air circuit involves, in particular, the compressed air circuit of a service brake. There can also be an additional compressed air circuit of the service brake. In particular, it is possible that the two compressed air circuits of the service brake are filled in parallel. Then in light of this specification the two service brake compressed air circuits can be regarded as the first compressed air circuit. The second compressed air circuit can be, in particular, a compressed air circuit that is allocated to a parking brake system and that also supplies additional compressed air consumers, for example, a trailer, with compressed air. Furthermore, there can also be other compressed air circuits, such as those that serve to supply a consumer with an especially high compressed air consumption. As a rule, when the compressed air consumer circuits are initially filled, such compressed air consumers are filled with compressed air only after the other compressed air circuits, in particular, the compressed air circuits of the service brake system, have been filled. However, the point in time at which such additional compressed air circuits are filled is not specified and can occur as a function of the requirements of the individual case.
A maximum pressure value corresponds to a maximum pressure, up to which a compressed air circuit is to be filled with compressed air. In this case it can be, for example, the maximum pressure intended for a service brake system and is typically 12.5 bar. A minimum set pressure can correspond to a minimum pressure, at which a compressed air circuit is regarded as functional. Due to legal provisions the minimum set pressure value for service brake systems is typically 7.5 bar. For the compressed air circuits allocated to the other compressed air consumer systems, the maximum pressure value and the minimum set pressure value can assume other suitable values. However, a minimum set pressure value does not have to be defined for all of the compressed air circuits.
An air dryer can have an air dryer cartridge that can be replaceable.
The moisture level of the air dryer can be determined by known methods. In particular, it can be provided that the moisture level is determined by a sensor or is calculated from the detected parameters. To this end, one or more suitable sensors and a suitable control unit can be provided. In order to determine the pressure in the compressed air circuits, it is also possible to use suitable sensors. According to this specification, a moisture level is parameterized by a moisture value. Hence, a higher moisture value corresponds to a higher moisture of the air dryer or rather the air dryer cartridge.
The moisture level can be defined as the so-called wetness level that corresponds to a volume of standard air conveyed through the air dryer. For example, a typical air dryer cartridge can have a capacity of 10,000 l of standard air, before it reaches its saturation degree at a wetness level of 10,000 l. An especially large air dryer cartridge can have, for example, a wetness level of 15,000 l, when it reaches its saturation level.
The invention relates to a method for regenerating a compressed air supply device of a commercial vehicle. In this case the compressed air supply device has an air dryer and is capable of supplying a first compressed air circuit, to which a predetermined maximum pressure value is assigned, and a second compressed air circuit with compressed air. According to this method, the first compressed air circuit is supplied with compressed air until the pressure in the first compressed air circuit has reached a predetermined target pressure value.
If at this point a moisture level of the air dryer exceeds a predetermined target moisture level, then the air dryer is regenerated with compressed air from the first compressed air circuit. The regenerating process is terminated, when the pressure in the first compressed air circuit has reached a predetermined limit pressure value or the moisture level of the air dryer has reached the target moisture level. Then the first compressed air circuit is supplied with compressed air until it has reached the target pressure value. If the moisture level of the air dryer is still greater than the target moisture level, then these steps are repeated. Otherwise, the second compressed air circuit is supplied with compressed air. Hence, the second compressed air circuit is not supplied with compressed air until the first compressed air circuit has reached the target pressure value, and the moisture level of the air dryer is at or below the target moisture level. Thus, when the second compressed air circuit is initially supplied with compressed air, the compressed air supply device is at a well-defined level. In particular, a low moisture level of the air dryer is guaranteed.
It can be especially practical for the target pressure value to be the maximum pressure value. Then the first compressed air circuit is filled up to the maximum level, before the filling operation of the second compressed air circuit is started.
A further development of the invention provides that the limit pressure value is greater than a minimum pressure value of the first compressed air circuit. As a consequence, the pressure in the first compressed air circuit never drops to the minimum set pressure value during the regenerating process.
It is especially practical if the target moisture level, or rather the associated target moisture value, corresponds to a dry air dryer. As a result, the air dryer is totally regenerated before the second compressed air circuit is supplied with compressed air. Hence, when the second compressed air circuit is initially supplied with compressed air, the air dryer can hold the largest possible amount of moisture. Consequently the saturation limit cannot be reached very quickly. Of course, it can be provided that during the filling operation of the second compressed air circuit an additional regenerating strategy is pursued. For example, it is contemplated to provide the method described below for the regenerating process.
A preferred embodiment provides that the parameters that are used are adapted during the process. In particular, it is provided that when the process steps are repeated, a modified target pressure value, a modified target moisture value, and/or a modified limit pressure value is (are) used. For example, a parameter can be easily changed by means of an electronic control unit by simply writing, for example, the modified values into a memory unit. This strategy enables a dynamic adjustment of the regenerating process to, for example, the changed environmental conditions or to changes in the compressed air system of the vehicle, for example, when after reaching a specific pressure value in the first compressed air circuit an additional compressed air circuit is to be supplied with compressed air by the compressed air supply device, before the second compressed air circuit is to be filled. Such a parameter change can occur especially in reaction to sensor signals.
Furthermore, it can be provided that the method or method steps are executed while the vehicle is running. In addition, it is self-evident that the legally prescribed pressures, for example, in the service brake, must be reached. As a result, it is possible for the driver to use the commercial vehicle as soon as the necessary conditions for operating the vehicle are filled, and he does not have to wait until the regenerating processes have been completed. This state can be achieved especially if, when the first compressed air circuit is a compressed air circuit of a service brake, the first pressure value is set above the minimum set pressure value prescribed by law for operating a vehicle, for example, at 9 bar. It is practical to set the limit pressure value, for example, at 8 bar, so that on reaching the first pressure value, at which a regenerating process can be carried out, even after a regenerating process that consumes the compressed air, the pressure in the service brake system is above the pressure value prescribed by law for use of the commercial vehicle.
In particular, it can be provided that when the compressed air circuits of the commercial vehicle are initially filled, the method is started or executed before the commercial vehicle is employed or rather upon startup of the commercial vehicle. In the event of such an initial filling operation, large amounts of compressed air are typically fed to the consumer circuits, and the air dryer is loaded correspondingly. If, however, the described method is used, then the moisture level of the air dryer remains low.
Furthermore, the invention provides a method for regenerating a compressed air supply device of a commercial vehicle. The compressed air supply device has an air dryer. According to the method, a first compressed air circuit of the commercial vehicle is supplied with compressed air. In this case the first compressed air circuit is fed a predetermined maximum pressure value. It is expedient that the first compressed air circuit can be a service brake system of the commercial vehicle.
However, it is also contemplated that the first compressed air circuit is allocated to another compressed air consumer system. If the pressure in the first compressed air circuit exhibits a predetermined first pressure value, and there is at least one predetermined first moisture level of the air dryer, then a regeneration of the air dryer is carried out with the compressed air from the first compressed air circuit. The regenerating process is terminated, when the first compressed air circuit exhibits a predetermined second pressure value that is below the first pressure value, or when there is a predetermined second moisture level of the air dryer. If at the end of the regenerating process the pressure in the first compressed air circuit is less than a target pressure value, then these steps are repeated. The first pressure value is less than the target pressure value, up to which the first compressed air circuit is supposed to be filled with compressed air. The second moisture level is below the first moisture level. This method allows a kind of intermediate regeneration to be carried out, before the target pressure value in the first compressed air circuit is reached. As a result, while filling the first compressed air circuit to the target pressure value, a regenerating process is generally executed, when there is adequate pressure in the first compressed air circuit, and a first moisture level of the air dryer is reached or exceeded. In contrast to the prior art, this strategy enables an early and frequent regeneration, as a result of which the moisture in the air dryer is held at a low level. The result is that, on the one hand, the moisture in the air dryer is prevented from reaching the saturation level. On the other hand, the moisture level is held generally low, thus raising the efficiency of the air dryer during normal operations.
In particular, it can be provided that when the compressed air circuits of the commercial vehicle are initially filled, the method is started or executed before the commercial vehicle is employed or rather upon startup of the commercial vehicle. In the event of such an initial filling operation, large amounts of compressed air are typically fed to the consumer circuits, and the air dryer is loaded correspondingly. If, however, the described method is used, then the moisture level of the air dryer remains low.
It is practical for the second pressure value to exceed a minimum set pressure value of the first compressed air circuit, so that the pressure in the first compressed air circuit is always above this minimum set pressure value. In this way the first compressed air circuit can also be used during the described method. This applies especially to the case of a service brake, where solely for reasons relating to the law the service brake system must exhibit a minimum pressure, so that the vehicle may be put into motion.
It is advantageous if the first moisture value and the second moisture value are below a saturated moisture value of the air dryer. Hence, the regenerating process is carried out, before the saturated moisture level in the air dryer is reached. The moisture level in the air dryer cartridge moves, according to the invention, between the first and the second moisture level and, hence, lies in a well-defined range. As a result, it is possible to set a moisture level in the air dryer that is efficient for operating the compressed air supply device. In this respect it can be especially advantageous if the first moisture value amounts to one-third the saturated moisture value or less in order to operate the air dryer with very little moisture.
In one advantageous embodiment a modified first pressure value and/or a modified second pressure value is (are) used between the regenerating operations or rather during an iterative process. It is also contemplated that a modified first moisture value and/or a modified second moisture value is (are) used. Hence, the parameters that are used are adapted during the process. A parameter change can be easily made, for example, by means of an electronic control unit in that the modified values are written, for example, into a memory unit. This strategy enables a dynamic adjustment of the regenerating process to, for example, the changed environmental conditions or to changes in the compressed air system of the vehicle, for example, when after reaching a specific pressure value in the first compressed air circuit an additional compressed air circuit is to be supplied with compressed air by the compressed air supply device. Such a parameter change can occur especially in reaction to sensor signals.
The invention can be further developed to the effect that the method or rather the steps of the method are executed while the vehicle is running. In addition, it is self-evident that the legally prescribed pressures, for example, in the service brake, must be reached. As a result, it is possible for the driver to use the commercial vehicle as soon as the necessary conditions for operating the vehicle are filled, and he does not have to wait until the regenerating processes have been completed. This state can be achieved especially if, when the first compressed air circuit is a compressed air circuit of a service brake, the first pressure value is set above the minimum set pressure value prescribed by law for operating a vehicle, for example, at 9 bar. It is practical to set the second pressure value, for example, at 8 bar, so that on reaching the first pressure value, at which a regenerating process can be carried out, even after a regenerating process that consumes the compressed air, the pressure in the service brake system is above the pressure prescribed by law for use of the commercial vehicle.
An especially preferred embodiment can provide that, furthermore, the compressed air supply device is capable of supplying a second compressed air circuit with compressed air. After the target pressure value in the first compressed air circuit has been reached, this embodiment provides that when the moisture level of the air dryer exceeds a predetermined target moisture level, then the air dryer is regenerated with compressed air from the first compressed air circuit. The regenerating process is terminated when the pressure in the first compressed air circuit has reached a predetermined limit pressure value, or the moisture level of the air dryer has reached the target moisture level. Then the first compressed air circuit is filled with compressed air until the pressure in the first compressed air circuit corresponds to the target set pressure. If at this point the moisture level of the air dryer is greater than the target moisture level, then the regeneration process is carried out again under the said conditions. If, however, the first compressed air circuit exhibits a pressure that corresponds to the target pressure value and if the moisture level of the air dryer is less than or equal to the target moisture level, then the second compressed air circuit is supplied with compressed air. Hence, a first compressed air circuit is supplied with compressed air, holding the moisture level in the air dryer low during the supplying process through the use of regenerating processes. If the first compressed air circuit is filled to a specific target pressure value, then the regenerating processes and supply processes are executed alternatingly. Not until there is both a target moisture level and a target pressure value is a second compressed air circuit supplied with compressed air. The result is that the second compressed air circuit is supplied with compressed air under precisely defined conditions regarding the moisture of the air dryer and the pressure level in the first compressed air circuit. In particular, filling the first compressed air circuit with compressed air can be achieved with a functional air dryer. Furthermore, it can be prevented that the air dryer quickly reaches a saturation level. This feature may be especially important when the first compressed air circuit is a part of the service brake system, and the second compressed air circuit is provided, among other things, for the parking brake system and, for example, the compressed air consumers of a trailer. It is also achieved that use of the vehicle can begin with an air dryer at a low moisture level, so that even in the event of a high compressed air consumption during use the saturation level is not reached.
It can be especially practical that the target pressure value is the maximum pressure value. Then the first compressed air circuit is filled up to the maximum level, before the filling operation of the second compressed air circuit is started.
Furthermore, it is advantageous that the limit pressure value is greater than a minimum pressure value of the first compressed air circuit. As a consequence, the pressure in the first compressed air circuit never drops to the minimum set pressure value during the regenerating process.
Furthermore, the invention provides an electronic control unit that is intended for controlling a compressed air supply device of a commercial vehicle and that is configured so as to control one of the methods described above.
In addition, the invention relates to a compressed air supply device that is intended for a commercial vehicle and includes an electronic control unit that is configured so as to control one of the methods described above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.